Tobacco smoke filter

ABSTRACT

A tobacco smoke filter element is disclosed which is designed to be accommodated in a cigarette, cigarette holder or the stem of a pipe and which is made of foamed, open cell nylon 6. The filter is made in rod form, has a skin of non-foamed nylon, a density of 1-5 pounds per cubic foot, a hardness of 75-95%, a resilience of 90-100% and a pressure drop across a 15mm length at a flow rate of 1500cc/mm. of between 2 and 8 centimeters of water gauge.

United States Patent Changani Jan. 21, 1975 1 TOBACCO SMOKE FILTER3,496,266 2/1970 Fairbanks 264/54 x 3,538,920 11/1970 Davis 131/10 [75]lnvemor- Pushpkumar Dewanma' 3,554,202 1/1971 .lamieson et al. 131 /269x Newport, England [73] Assignee: Monsanto Chemicals Limited, FOREIGNPATENTS OR APPLICATIONS London England 6,514,911 /1967 Netherlands131/269 [22] Filed: June 1973 Primary Examiner-Me1vin D. Rein 21 3 9Attorney, Agent, or Firm-Joseph S. Nelson; Edward P. Grattan; James C.Logomasini Related U.S. Appllcatlon Data 3 x p I, [63] Continuation ofSer. No. 22,068, March 23, 1970,

abandoned. [57] ABSTRACT A tobacco smoke filter element is disclosedwhich is [52] 11.8. C1. 131/269 designed to be accommodated in acigarette, cigarette [51] Int. Cl A24d 1/04 holder or the stem of a pipeand which is made of [58 Field of Search 131/269, 10.5, 10.7; foamed,open cell nylon 6.

260/25 N; /522 528 The filter is made in rod form, has a skin ofnon-foamed nylon, a density of l-S pounds per cubic [561 Referencesfoot, a hardness of -95%, a resilience of UNITED STATES P S and apressure drop across a 15mm length at a flow 2,268,160 12/1941 Miles131/269 UX rate of 1500cc/mm. of between 2 and 8 centimeters of3,127,373 3/1964 Guttag... 131/269 X water gauge. 3,234,152 2/1966Fuller 260/25 N 3,327,031 6/1967 Boyer et a1. 264/53 2 Chums, N0Drawings TOBACCO SMOKE FILTER This is a continuation of application Ser.No. 22,068, filed Mar. 23, 1970 now abandoned. I

This invention relates to filtering elements, and particularlysmoke-filtering elements adapted for use with smoking devices such as acigarette or pipe. It also includes certain new filtering elements ofgeneral application.

It has already been proposed to insert a filtering element in the end ofa cigarette in order to prevent flakes of tobacco from entering themouth and to reduce the consumption by the smoker of certain undesirablesubstances present in the smoke. Similarly, it has been proposed toplace a filtering element in the stem of a pipe to reduce the entry ofunwanted combustion products into the respiratory tract. A disadvantageof such proposals has been that filters efficient enough to have auseful absorptive effect comprise a relatively large amount of material,that is to say they have a high density, so that they are quiteexpensive when made by the million. Moreover, when filtering elementsare made on this scale their manufacture must be rapid and convenient.Thus the production of the filtering element should involve a minimumnumber of steps before each filtering element is ready to beincorporated in the smoking device.

A process has now been developed which can conveniently be used to makesmoke-filtering elements on a large scale. Also the smoke-filteringelements produced by the process show a useful absorptive effect atrelatively low densities.

The process is one for the production of a smokefiltering element havinga cross-section suitable for use with a smoking device such as acigarette, cigarette holder, or pipe, which comprises extruding a rod offoamed synthetic polyamide resin having a substantially open-cellstructure, the rod having a transverse cross-section substantiallycorresponding to that desired in the final element.

The smoke-filtering elements of the invention are preferably cut orotherwise divided from a rod having an outer skin. They can be cut intopieces that are the length of an individual filter or for example, intopieces that are a simple multiple of this length, preferably from 2 totimes the length of an individual filter.

According to another aspect of the invention there is provided afiltering element which comprises a foamed nylon 6 (polycaprolactam)having a substantially opencell structure.

The synthetic polyamide is a thermoplastic resin material containingamide groups as part of the polymer chain of the resin molecule It canfor example be produced by the polycondensation of a diamine and adicarboxylic acid, or of a salt of such an amine and such an acid, bythe self-polycondensation of an -aminocarboxylic acid or by thepolymerization of a lactam. Examples of well-known polyamides are nylon6 (polycaprolactam), nylon 66 (polyhexamethyleneadipamide, normallyproduced by the self-polycondensation of the salt ofhexamethylenediamine and adipic acid known as nylon 11 nylon 11(poly-11- aminoundecylenic acid) and nylon 610(polyhexamethylene-sebacamide); and blends of these polyamides can, ofcourse also be used. The preferred polyamide is nylon 6. Preferably themolecular weight of the polyamide is between 10,000 and 20,000 forexample from 12,000 to 15,000.

The polyamide is in the form of a foam having a substantially open-cellstructure, that is to say, at least 50% of the cells of the foamintercommunicate with neighboring cells. Preferably at least of thecells are open in this way, and since in practice it is difficult tomake a foamed nylon in which more than 95% of the cells are open thepreferred range is 6095%, and very often from to 90%. Preferably most ofthe cells have a diameter within the range 0.002 to 0.02 inch, morepreferably from 0.005 to 0.01 inch.

The density of the foam is preferably low, usually not more than 10pounds per cubic foot and preferably from 1 to 5 pounds per cubic foot.Between 2 and 3 pounds per cubic foot is often a very suitable density.

Two important properties, particularly where the element is intended foruse as a cigarette filter-tip, are the hardness and resilience of thefoam. These can be measured by means of an lnstron compression testingmachine, applying a progressively increasing load to a cylindricalsample 15 millimeters long and 8 millimeters in diameter, the load beingapplied to opposite sides of the cylindrical surface by flat steelplatens advanced towards each other at a relative speed of 0.2 inchesper minute. The hardness is the diameter of the sample measured at aload of 300 grams and expressed as a percentage of the originaldiameter, while the resilience, similarly expressed, is the diameter ofthe sample after the load has been released for several seconds.

Preferably the hardness is from 50 to 95%, more preferably from to 95%and very often from to Preferably the resilience as measured by theabove test is from 80 to more preferably from 90 to 100% and very oftenfrom 98 to 100%.

For use in a cigarette, the smoke-filtering element is preferablycylindrical in shape and of the same diameter as a cigarette and forexample about 0.374 to 0.75 inch in length although other shapes andsizes can optionally be used. For example, for use in a Turkishcigarette, the element would be of oval cross-section. For use in apipe, the smoke filtering element is preferably cylindrical if requiredto fit in the stem, although other shapes can be used if desired.

The pressure drop across the smoke-filtering element is preferably low,for example below 15 centimeters of water gauge measured for a sample 15millimeters in length, at a flow rate of 1500 cubic centimeters perminute. A particularly acceptable range of pressure drop is between 2and 10 centimeters of water.

The foamed polyamide is produced by an extrusion method which allows theproperties and dimensions of the rod, and hence the smoke-filteringelements cut from it, to be carefully controlled. The shape and size ofthe die orifice are a determining factor, and these are chosen so as togive the desired product. For example, filtering-elements incorporatedin cigarettes are usually of circular cross-section and can be cut froma cylindrical rod of foamed resin extruded from a circular die orifice.Finer control of the diameter of the rod can sometimes be obtained bydrawing it, although, of course, the drawing should not be such as todestroy the desirable properties of the foamed resin. The extruded rodis preferably given a hard outer skin which makes the filtering-elementscut from the rod more durable. It can be seen that the process of theinvention is a simple one giving filtering elements ready for directincorporation into the smoking device. Unlike some conventional methodsthere is no need to use adhesive in forming the filtering element intoan appropriate shpae or to use material in the form of a tightly rolledcylinder.

In the process of making the foamed filter one needs to employ a blowingagent, which can be a gas or vapor under normal atmospheric conditionsbut is preferably a volatile liquid. Preferably it possesses anappreciable solubility in the polyamide under conditions of elevatedpressure and temperature such as those present in an extruder. Thepreferred blowing agents are lower alcohols such as methanol, ethanoland the propanols, but other examples are lower ketones, for exampleacetone, and lower hydrocarbons such as butane, pentane or isobutylene.If a hydrocarbon is used, a volatile plasticizer, for example methanol,is preferably also present The blowing agent can also be a chemicalblowing agent, which can for example be a bicarbonate such as forexample sodium bicarbonate or ammonium bicarbonate, or an organicnitrogen compound that yields nitrogen on heating, such as for exampledinitrosopentamethylenediamine or barium azodicarboxylate. From 3 to 30%especially from 7 to 20% by weight based on the weight of the resin isoften a suitable proportion of blowing agent.

Preferably the blowing agent is employed in conjunction with anucleating agent, which assists in the formation of a large number offine cells. A wide range of nucleating agents can be employed, includingfinely divided inert solids such as for example talc, silica or alumina(if desired in conjunction with an adhesive substance such aspolyethylene glycol or a mineral oil), or small quantities of asubstance that decomposes at the extrusion temperature to give a gas canbe used. An example of the latter class of nucleating agents is sodiumbicarbonate, if desired in conjunction with a weak acid such as forexample tartaric or citric acid. A small proportion of the nucleatingagent, for example up to 5% by weight of the resin, is usuallyeffective. Often the amount of nucleating agent employed is in the rangeof from 0.1 to 5% by weight, preferably from 1 to 2% by weight.

The extrusion temperature (that is the temperature of the die and theresin within it) needs to be below the crystalline melting point of thepolyamide (making a suitable allowance for the depressant effect of theblowing agent), and is preferably between 180C. and 250C. An extrusiontemperature from 190C. to 210C. is often suitable for nylon 6 while200C. to 240C. is often suitable for nylon 66. Higher temperatures, forexample up to 300C., can exist in the extruder barrel, particularlywhere the blowing agent is directly injected into the molten polyamide.For example a barrel temperature of 220C. to 250C. is often suitable fornylon 6, while for nylon 66 a barrel temperature of 265C. to 280C. ismore suitable.

Production of the requisite open-cell structure can be ensured bysuitable choice of extrusion conditions. For example the surface of theextruding foam can be cooled or the temperature of the extrudingmaterial controlled so as to form a surface skin strong enough toprevent collapse as the pressure within the cells falls. The cells wallsbecome perforated during the foaming process and this is assisted by therelatively high fluidity of the polyamide when plasticized with blowingagent.

A nucleating agent can also assist in cell-wall rupture and for examplea mixture of talc and polyethylene glycol has been found to beparticularly useful in this respect.

As described above, the invention includes a filtering element whichcomprises a foamed nylon 6 (polycaprolactam) having a substantiallyopen-cell structure.

The foamed nylon 6 can be produced by molding or by extrusion methods(referred to above). When a molding method is used the products can bedirectly molded in the desired shape so that there is no need forfurther treatment, or it can be cut or otherwise divided into pieces,such as strips, to give a filtering element of appropriate shape andproperties.

The foamed nylon 6 can also be produced by extrusion techniques. It isoften convenient to extrude the foamed nylon 6 in the form of a rodwhich can then be cut or otherwise divided into pieces of the desiredlength. Thus a preferred filtering element is in the form of a rod offoamed nylon.

The nylon 6 filtering elements are applicable to general filtration, forexample air conditioning, central heating, mining, oil or waterfiltration, and so on. They are particularly useful in filteringentrained dust particles from streams of air or other gases, and can,for instance, be employed as smoke-filtering elements.

One preferred form of filtering element comprises a number of rods orstrips of foamed nylon 6 packed together in parallel arrangement. Suchfiltering elements find many industrial applications for each of which afiltering element having appropriate properties can be built up. Forexample the rate of filtration of the filtering element party depends onthe cross-sectional area of the element and this can be varied accordingto the number of rods of foamed nylon 6 packed together. In addition thefiltering action is controlled by the length of the rods employed; thelonger the rods, the more efficient the filtering action. However, apractical limitation is put on the length of the rods by the need,'inmany cases, to reduce the pressure drop across the filtering element toa sufficiently low value.

The rods of foamed nylon 6 are preferably packed together in a matrix,for example an adhesive, or by exerting pressure on the packed rods sothat air gaps between them are excluded.

This invention is illustrated by the following Examples.

EXAMPLE 1 This Example describes a process for producing acigarette-filter element. All parts are by weight.

A blend of 100 parts of nylon 6, 0.1 part of polyethylene glycol and 2parts of finely-divided talc was fed to an extruder fitten with acircular orifice die of diameter l/l6 inch and land 3/16 inch. 16.5Parts of methanol were injected into the molten nylon at a temperatureof 278C. and the resulting mixture was cooled as it passed along theextruder barrel, the extrusion temperature being 193.5C.

There was extruded a rod of foamed nylon, of overall density 2.5 poundsper cubic foot, about 0.25 inch in diameter, having an outer imperviousskin enclosing a mass of intercommunicating open cells of averagediameter 0.009 inch. About to of the cells were open. The foam had 86%hardness and 99% resilience as measured by the test described above.

The rod was chopped up into pieces about 0.7 inch long and there wereused as filter tips for cigarettes. When the cigarettes were smoked, itwas found that the tips had a pleasing resilience and did not have anyadverse effects on the smokes taste. Neither did they offer a detectableresistance to the flow of smoke. When the elements were later cut upthey were found to have removed a considerable quantity of tar from thesmoke, comparable with that removed by a conventional cellulose acetatetow filter having a density 9.75 pounds per cubic foot.

EXAMPLE II This Example describes a filtering element according to theinvention.

A rod of foamed nylon 6 having the properties described in Example I andproduced by the process described in that Example, was chopped intopieces 4 inches long. Adhesive was applied to that outer skin of 80 suchrods and they were packed together in parallel arrangement. A slightpressure was applied to ensure good adhesive contact and to exclude airgaps and channels between the rods.

The filtering element so formed showed a pressure drop across its endsof 65.3 centimeters of water, as measured by a water manometer at an airflow rate of 1500 cubic centimeters per minute. The filtering elementwas tested for its properties of extracting tar from cigarette smoke andthese were found to be excellent.

What is claimed is:

1. An improved foamed open cell tobacco smoke filtering element theimprovement comprising, foamed Nylon 6 having from 60 to 95% openperforated cell structure, a density of from 1 t0 5 pounds per cubicfoot and said cells having a diameter of about 0.002 to about 0.02 inch,said filtering element having the form of an extruded rod having animpervious substantially nonfoamed Nylon 6 skin and traversecross-section substantially corresponding to the final element and whichcoresponds to the diameter of the cigarette, the cigarette holder or thestem of a pipe in which it is to be fitted and the hardness of the rodis from to the resilence of the rod is from 90 to and the pressure dropacross said rod about 15 millimeters in length at a flow rate of 1500cubic centimeters per minute is between 2 and 8 centimeters of watergauge providing low resistance to the flow of smoke through the filterelement.

2. A smoking device comprising the smoke filtering element of claim 1.

2. A smoking device comprising the smoke filtering element of claim 1.